Electrical displacement-resistance contact member and method of manufacture thereof



April 1949. H. c. PAs|Nl m-AL 2,463,344

ELECTRICAL DISPLACEMENT-RESISTANCE CONTACT MEMBER AND METHOD OFMANUFACTURE THEREOF Filed Oct. 14. 1944 2 Sheets-Sheet 1 PERCENTRESISZ'HNCE PERCENT LENGTH.

April26, 1949- H. c. PASlNl ETAL 2,468,344

ELECTRICAL DISPLACEMENT-RESISTANCE CONTACT MEMBER AND METHOD OFMANUFACTURE THEREOF 2 Sheets-Sheet 2 Filed Oct. 14, 1944 SERVO-AMPLIFIER UNIT INVENTORS.

Patented Apr. 26,1949

asses ELECTRICAL DISPLACEMENT-RESISTANCE CONTACT MEMBER MANUFACTURETHEREOF AND METHOD OF Harold C. Pasini, Fair Lawn, N. 1., and George M.Heckel, Elmhurst, N. 1., assignors to Fairchild Camera and InstrumentCorporation, a corporation of Delaware Application October 14, 1944,Serial No. 558,720

6 Claims. (Cl. 201-62) This invention relates to electrical contacts rorresistors and to the method of their manufac-' ture and, while it is ofgeneral application, it is particularly useful in a system for windingprecision resistors including circuit means for continuously comparingthe resistor being wound with a variable portion of a referenceresistor, together with means for controlling the winding of theprecision resistor by such circuit means, and the invention will bedescribed as embodied in such a system.

In various electrical systems it is frequently desirable to procure, inresponse to a given displacement of an element, a resistance value whichis continuously variable in accordance with an accurately predetermineddisplacement-resistance characteristic over the extent of suchdisplacement. In general this presents a problem, even when a lineardisplacement-resistance characteristic is desired, as resistors withaccurate linear displacement-resistance characteristics often are noteconomically feasible. In installations in which non-lineardisplacement-resistance characteristics are desired, the problem is moredifficult and in general requires some nonlinear driving mechanism, suchas a mechanical cam, interposed between the movable elements and theadjustable resistor. Not only is the accurate construction of such amechanical cam costly but in some cases the steepness of the requireddisplacement-resistance characteristic involves excessive cam pressureangles which limit the sensitivity and accuracy of the system of whichthe cam forms a part.

It is an object of the invention, therefore, to provide a new andimproved electrical contact for resistors by means of which any desireddisplacement-resistance characteristic may be obtained, at the same timeobviating the limitation of the prior art arrangements for procuringsimilar results.

It is another object of the invention to provide a new and improvedelectrical contact for resistors by means of which any desireddisplacement-resistance characteristic may be obtained and one which issimple and economical in construction and accurate and sensitive inoperation.

It is a further object of the invention to provide a new method ofmanufacture of electrical contacts for resistors of the type described.

-- In accordance with the invention, an electri- K cal contact for aresistor having a predetermined pended claims.

relief portionhas a configuration related to the displacement-resistancecharacteristic of the resistor. By the term linear-developed surface" asused herein and in the appended claims is meant a regular surfacedeveloped by a given line moving around or along a given generatingpath, well known examples being plane surfaces and circular cylindricalsurfaces.

Further in accordance with the invention, the method of manufacturing adisplacement-resistance contact member of the type described from asheet of conductive material comprises producing on one surface of saidsheet a graph of the desired displacement resistance characteristic,disposing a wire along said graph, and rolling the sheet and wire tocause the wire to emboss a relief portion on the opposite surface of thesheet. V

Further in accordance with the invention, an electrical contact memberof the type described is embodied in a system for winding precisionresistors including circuit means for continuously comparing theresistor being wound with a variable portion of an elongated referenceresistor and means for controlling the winding of the precision resistorby such circuit means, the electrical contact member being provided forincluding a variable portion of the reference resistor in the circuitmeans.

v For a better understanding of the invention, together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawings the ap-' while itsscope will be pointed out in Referring now to the drawings, Fig. 1 is agraph illustrating a type of displacement-resistance characteristicwhich may be desired; Fig. 2 is a top view of an electrical contactmember to which the characteristic of Fig. 1 is transposed; Fig. 3 is acircuit diagram, partly schematic, of a complete system for windingprecision resistors with any desired displacement-resistancecharacteristic and embodying the electrical contact of the invention;while Figs. 4a and 4b are side and end views, respectively, of amodified form of electrical contact member involving a rotational ratherthan a translatory displacement.

Referring now to the'drawings, there is represented an electricalcontact member for deriving from a reference resistor in response to agiven displacement a continuously variable resistance value having apredetermined displacement-resistance characteristic, as represented bya continuously variable portion of the reference resistor, together witha system for winding precision resistors in which such electrical cam isutilized. It is assumed that it is desired to obtain adisplacement-resistance characteristic of a predetermined shape. Thischaracteristic is first plotted on appropriate coordinate paper, asrepresented in Fig. l, in which the abscissas represent the percentageof. length of the resistor, that is, of the given displacement, and theordinates represent the percentage of maximum resistance. Thecharacteristic of Fig. 1 is then reproduced on a conductive metallicmember or template having a linear developed surface, such as the planesurface of member 9 of Fig. 2. The characteristic of Fig. 1 may betransferred to the template of Fig. 2 by photo-engraving, or likephotographic process, by manually depositing a fine and uniform ridge ofconductive material thereon, by embossing, or by any other equivalentprocess. Preferably the member 9 is a thin sheet or a thick foil ofconductive material such as aluminum and the desired characteristic istransferred to one surface thereof by tracing the curve of Fig. 1thereon with carbon paper. Thereafter a fine wire, for example No. 18gauge, is disposed along the traced characteristic and, adhesivelyretained in place, as by an adhesive tape. This sheet is then runthrough a pair of rollers, the roller engaging the wire side of themember 9 being rigid and the other being semiresilient, such as hardrubber, so that the wire indents or embosses a relief portion on theopposite surface of. the member I. In anyevent, there is developed onmember 9 a relief portion 9a, preferably lineal as illustrated, whichhas a configuration which is a reproduction of the characteristic ofFig. 1.

The member 3 of Fig. 2 can then be utilized in a system for windingprecision resistors such as represented in Fig. 3, which is of the samegeneral type as described and claimed in the copending application ofHenry E. Hale, entitled Method of and apparatus for winding precisionresistors and resistors formed thereby, Serial No. 514,894, filedDecember 20, 1943. This system includes circuit means for continuouslycomparing the resistor being wound with a variable portion of anelongated reference resistor and means for controlling the winding ofthe precision resistor by such circuit means. Specifically, the systemof Fig. 3 comprises a winding mechanism consisting of a pair of holdersl and H supported in bearings I2 and i 3, respectively, adaptedresiliently to hold an elongated resistor card ll of insulationmaterial, the holder il being biased into engagement with the card I4 bymeans of a spring 15. A manually operable knob I8 is provided forinitiating a few turns on the card I. The winding mechanism alsoincludes means for winding resistance wire on the card I to form aresistor R and consisting of a feed-wire holder I! in which is mounted aspool l8 carrying a supply of resistance wire IS, the wire being passedthrough a guide and tensioning element 20 constituting an extension ofthe holder H. The wire after passing through the element 20 is fed tothe resistor card 14 in a. conventional manner to form a resistorthereon. The card It is adapted to be rotated at constant speed by meansof a suitable motor 2i and reduction gearing 22. Electrical connectionsare made to the resistor R during winding by means of a sliding contact20a attached to guide 20 and bearing on the wire I! as it is fed to cardH and a brush Ila bearing on the conductive holder l i which isconnected to a terminal Ha on card I or to any other suitable connectionto the starting point of the winding forming the final resistor R.

The winding apparatus also includes an advancing means for producingrelative transverse movement between the resistor card I4 and thefeed-wire holder l1 during rotation of the card I to form a resistorthereon. This advancing means comprises a feed screw 23 engaging athreaded portion lla of the holder 11 and driven by a follow-up motor 24through reduction gearing 25. The feed screw 23 is Journalled insupports 28, 26 which also hold a guide rod 21 engaging an extension Nbof the holder I! to maintain steady transverse movement of the holderII.

In order to impart to the resistor R, formed as described, adisplacement-resistance characteristic which is an accurate reproductionof that of Fig. 1 and of the relief portion 9a of member 0, the systemcomprises means including the electrical contact of the invention forcontinuously comparing the resistance value of the resistor R during thewinding operation with that of a corresponding varlable portion of areference standard resistor. Specifically, a reference standard resistor30 is mounted in a yoke ll, including guide ways Ila sliding on a pairof guides 32 supported in a frame II. The yoke II also includes athreaded nut I I b engaging a threaded rod 34 comprising an extension ofa shaft 34a iournalled in the frame 33. The frame II is disposed toslide the reference resistor 10 over the member 3 maintaining acontinuous contact between the resistor in and the relief portion 9a ofthe member 9, the frame 3| and its operating mechanism thus comprisingmeans for producing relative translatory motion between the member 8 andthe resistor 30.

The system of Fig. 3 also includes a pair of output terminals comprisingthe terminal lb connected to the relief portion 8a of the meml, whichconnection, in case of homogeneous metallic construction, may constitutea connection to any point of the member 9, and the terminal I lcconnected to an adjustable contact Ild engaging a conductive portion ofthe frame 3! in electrical connection with a fixed point on thereference resistor 30, preferably the end or zero point of the resistor.The portion of the resistor wound on the card H at any moment iscompared with the portion of the reference resistor 30 included betweenterminals lb and tie by means of an electrical bridge including as twoadjacent arms the corresponding portions of the reference resistor 30and the resistor R and as the other two arms resistor elements II and 36of predetermined relative resistance values, the bridge being connectedto compare such portions of resistors l4 and 30 by electricallybalancing them against each other in the bridge circuit. To this end,one secondary winding 31 of a supply transformer II is connected acrossone diagonal of the bridge circuit described, while the other diagonalof the bridge circuit is connected to the input circuit of aservoarnplifier unit 3!. The power supply circuit of the amplifier unitI. is energized from a secondary winding ll of the supply transformerII, while the output circuit of the amplifier 3! is connected toenergize the follow-up motor 24 which produces a relative transversemovement between the wire-feed apparatus and the resistor card ll.

In order to effect movement of the resistor ll over the relief portionla of the member 9, corresponding to the given range of displacement ofthe yoke 3|, for selecting a continuously varithe bride circuit.

\ and de-energization of the several circuits of the apparatus tov startand stop the winding operation. If desired, suitable automatic stoppingdevices well known in the art may be included automatically to stop thesystem upon the completion of winding of any resistor R.

Referring now to the operation of the system of Fig. 3 described above,it will be assumed that theresistor card I4 is placed in the holder anda few turns wound thereon by means of the menually actuated knob ituntil the wire reaches the terminal No or other equivalent connection tothe starting point of the winding. It is assumed that, at this point,the adjustable yoke ii is at the extreme left-hand limit of itsmovement, in which position all of the resistor 30 is cutout of Assumingthat at this point there is a small amount of resistance, which may beinherent circuit resistance with or without an added resistance elementapproximately to balance the bridge circuit under these conditions andwhich is represented by dotted-line resistor R in circuit with thereference resistor 30, the bridge circuit comprising elements R, R0, 35,36 is slightly unbalanced. The unbalance voltage is applied to theamplifier 39, is amplified therein, and applied to the follow-up motor24, initiatinz transverse movement of the feed-wire holder I! to startthe formation of the resistor R on the card l4. At the same time thefollow-up motor through the gearing 25, 42, 43 actuates the threaded rod34 to advance the yoke 3|, which is effective to move the referenceresistor 30 over the relief portion 9a of the conductive member I toinclude continuously increasing portions of the resistor 80 in thebridge circuit.

When the apparatus described has reached a state of equilibrium, therewill be a substantially constant difference in resistance between theportion of the reference resistor 30 included in the bridge circuit andthe portion of the resistor wound on card I, this difference being onlythe small amount required to maintain the unbalance of the bridgecircuit sufficient to actuate the follow-up motor 24 for advancing thefeed-wire holder l1 relative to the resistor card I. Since the card I4is rotated at constant speed by motor II to wind a given number of turnsper unit of time, while the wire-feed holder l1 and the yoke Ii areadvanced synchronously but at a variable speed by motor 24 to maintainthe bridge circuit in balance, the amount of resistance wire wound onthe card l4 per unit of transverse movement of the feed-wire holder I1is varied to control the displacement-resistance characteristic of theresistor R. The gearing 25 is preferably one of a number ofinterchangeable gearings to provide a different range of rates ofadvance of the holder H for each wire size used, the rate within eachrange being controlled as described. This arrangement causes the systemto operate with a minimum unbalance signal and maximum accuracy.

The displacement-resistance characteristic of the resistor R is thusaccurately predetermined by the characteristics of the referencestandard ll and the electrical contact member. I and the referenceresistor II. The configuration of the relief portion 8a of the member 0is so proportioned in relation to the displacement-resistancecharacteristic of the reference resistor as to develop between theoutput terminals 9b, tie the desired predetermined resistancecharacteristic which is duplicatd in the resistor R. being wound. Incase the reference resistor III has an accurately lineardisplacement-resistance characteristic, the configuration of the reliefportion la will correspond exactly to the desired displacementresistance characteristic. However, in practice it will generally bemore feasible to adopt a reference standard having a characteristicwhich may be either linear or non-linear but which preferablyapproximates that desired and then represent in Fig.1 and transfer tothe member of Fig. 2 a measured calibration curve effective to convertthe actual displacement-resistance characteristic of the referenceresistor II to the desired displacement-resistance characteristic. Inany event, the displacement-resistance characteristic of the resistor Rwill be substantially matched to the resistance characteristic appearingat the terminals 912, lie, which is determined by the electrical camcomprising the reference resistor 30 and the member 9. i

In Figs. 4a and 4b are represented a modified form of the electrical camof the invention in which the conductive contact member having alinear-developed surface is, in this instance, a cylindrical conductivemember 5|! having a lineal relief portion 50a formed thereon. The member50 is mounted for rotation on a suitable shaft 5i supported in bearings52, 52 and includes an electrical connection 50b to a slip ring 53having a cooperating brush 53a. The reference resistor 30 is held insuitable holders 54 and the mounting of the elements is such that, asthe shaft 5| is rotated to produce relative rotation between the member50 and the resistor 30, the relief portion 50a is biased into continuouscontact with the reference resistor 30. The operation of themodification of Fig. 4a is in other respects similar to that describedin connection with Fig. 3.

Thus, it is seen that by means of the electrical contact of theinvention embodied in a resistor winding system, a resistor having anon-linear displacement-resistance characteristic of any desired taperor steepness may be readily formed without the disadvantagesaccompanying the use of a mechanical cam with a large pressure angle.

While there have been described what are at present considered to be thepreferred embodiments of the invention, it will be apparent to thoseskilled in the art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed as new is:

1. The method of manufacturing a displacement-resistance contact memberof a sheet of conductive material which comprises, producin on onesurface of said sheet a graph of the desired displacement-resistancecharacteristic, disposing a wire along said graph, and rolling saidsheet and said wire to cause said wire to emboss a relief portion on theopposite surface of said sheet.

2. The method of manufacturing a displacement-resistance contact memberof a. sheet of conductive material which comprises, plotting a graph ofthe desired displacement-resistance cam characteristic, transferringsaid graph to one surface of said sheet, disposing a wire along saidtransferred graph, and rolling said sheet and said wire to cause saidwire to emboss a relief portion on the opposite surface of said sheet.

3. The method of manufacturin a displacement-resistance contact memberof a sheet of conductive material which comprises, producing on onesurface of said sheet a graph of the desired displacement resistancecharacteristic, disposing a wire along said graph, adhesively retainingsaid wire in place on said surface, and rolling said sheet and said wireto cause said wire to emboss a relief portion on the opposite surface ofsaid sheet.

4. In a system for winding precision resistors including circuit meansfor continuously comparin the resistor being wound with a variableportion of an elongated reference resistor and means for controlling thewindin of said precision resistor by said circuit means, an electricaicontact member for including a variable portion of said referenceresistor in said circuit means comprising, a member having an integrallinear-developed surface and a conductive relief portion thereon, meansfor producing relative motion between said member and said referenceresistor whiie maintaining contact between said relief portion and saidresistor, and output terminals connected to said relief portion and to afixed point on said reference resistor, the configuration of said reliefportion being so proportioned in relation to the displacement-resistancecharacteristic of said reference resistor as to develop the desireddisplacement-resistance characteristic between said terminals.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATE. PATENTS Number Name Date 2 3,320 Crooke Aug. 29, 1882844,380 Marwich Feb. 19, 1907 1,102,483 Dolson July 7, 1914 1,940,102Roberton Dec. 19. 1933 1,971,238 Silling Aug. 21, 1934 2,095,199 SpeedOct. 5, 1937 2,220,951 Borden Nov. 12, 1940 FOREIGN PATENTS NumberCountry Date 265,706 Great Britain Feb. 17, 1927

